The invention concerns an electrical switch to switch on and off an electrical circuit by commutating a switchoff current from a continuous current path to an extinction current path, and vice versa, and the breaking or restoring respectively of the continuous current path by the relative motion between two contact members, where a first contact is arranged in region that is under a relatively low gas pressure, and a second contact is arranged in a pressure chamber which can be brought into communication with said region by way of a narrow nozzle opening and within which can be generated a higher gas pressure relative to that of said region for the purpose of quenching by blasting a main arc arising across the contacts during the switchoff.
Electrical switches of this type have been known for some time and are employed primarily as a high-voltage power circuit-breaker, a species of which is described in the Brown-Boveri "Mitteilungen," No. 4-1976, namely, a SF.sub.6 high-voltage power switch type ELF for outdoor installation. This switch uses as a quenching and insulating medium sulphur hexafluoride (SF.sub.6) which has been utilized with great success in many encased systems because its characteristics are very suitable for this specific purpose. This switch employs the compression piston principle where the quenching pressure, necessary for the extinction of the arc, is generated in a compression piston during the circuit-breaking movement.
The switch unit comprises a stationary contact, a moving contact driven by a switch rod with spring-actuated or pneumatic power, with the compression cylinder and the arc contacts which become functional at the time of circuit-breaking.
During the circuit-breaking operation the driven contact moves downward toward the switchoff position and the compression within the blast piston space will begin. This is followed by a separation of the continuous current contacts a commutation of the current to the arc contacts, a separation of the arc contacts and the formation of the arc across the arc contacts, followed by the blasting of the arc by the gas compressed by the blast piston and the extinction of the arc. The switchoff position is finally reached and the blasting is terminated.
The gas required for the blasting is compressed within a pressure chamber surrounding one of the drive contacts, with the compression taking place throughout the entire switch travel at decreasing compression volume and increasing resistance. The compression work must therefore be achieved externally in the form of drive energy. The generated gas pressure is therefore a burden for the drive of the switch unit and the magnitude of the differential pressure will depend on the switch travel. The volume of the pressure chamber and the motive power required are also very substantial.